Preparation of meixnerite (Mg–Al–OH) type layered double hydroxide by a mechanochemical route

We have attempted to synthesize the meixnerite (Mg–Al–OH) type layered double hydroxide (LDH) by a two step milling operation of a mixture of Mg(OH)₂ and Al(OH)₃ with water. In the first-step, a mixture of the starting materials was milled for 1 h without water, and the product prepared in the first-step was milled for 2 h with water in the second-step milling operation. The milled products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermo gravimetric-differential thermal analyses with mass spectroscopy (TG-DTA/MS). The surface morphology was characterized by scanning electron microscopy (SEM). Meixnerite with a small amount of carbonate was successfully synthesized mechanochemically at ambient conditions by milling for only 3 h in a planetary ball mill.     

Sintering behavior of mechanically alloyed Ti-48Al-2Nb aluminides

Ti-Al intermetallics have been produced using mechanical alloying technique. A composition of Ti-48Al-2Nb at % powders was mechanically alloyed for various durations of 20, 40, 60, 80 and 100 h. At the early stages of milling, a Ti (Al) solid solution is formed, on further milling the formation of amorphous phase occurs. Traces of TiAl and Ti₃Al were formed with major Ti and Al phases after milling at 40 h and beyond. When further milled, phases of intermetallic compounds like TiAl and Ti₃Al were formed after 80 hours of milling and they also found in 100 h milled powders. The powders milled for different durations were sintered at 785°C in vacuum. The mechanically alloyed powders as well as the sintered compacts were characterized by XRD, FESEM and DTA to determine the phases, crystallite size, microstructures and the influence of sintering over mechanical alloying.     

Comparative study on sintering behavior of Al86Ni6Y4.5Co2La1.5 mechanically alloyed amorphous powder and melt-spun ribbon

In this research work, the sintering characteristics of Al₈₆Ni₆Y_4.5Co₂La_1.5 mechanically alloyed amorphous powders and milled melt spun ribbon have been compared. Mechanically alloyed amorphous powders were synthesized via 200?h high energy ball milling. Melt spun ribbons were synthesized by single roller melt spinning technique and grounded to powder form by ball milling. Mechanically induced partial crystallization occurred in the ribbons during milling. Significantly higher amount of contaminations such as carbon, oxygen and iron were observed in the mechanically alloyed amorphous powders compared to the milled ribbons. Both powders were consolidated via spark plasma sintering. Superior particle bonding was found in the sample consolidated from milled ribbons, ascribed to the lower amount of contamination that could not effectively restrict the viscous flow and diffusion of atoms. Various complex crystalline phases evolved in the sample consolidated from milled ribbon particles due to the presence of crystalline phases in the powders which acted as nucleation sites, whereas the amorphous phase was mostly retained in its counterpart. Vickers microhardness of the consolidated alloys from milled ribbon and mechanically alloyed amorphous powders were 3.60?±?0.13?GPa and 2.53?±?0.09?GPa, respectively. The higher hardness in the former case was attributed to the superior particle bonding and distribution of hard intermetallic phases in the amorphous matrix.     

Structural evolution during mechanical alloying and annealing of a Nb-25at%Al alloy

Mixtures of pure elemental Al and Nb powders of Nb-25at%Al composition was mechanically alloyed, and structural evolution during high energy ball milling has been examined. Al dissolved in Nb from the early stage of the ball milling, and amorphization became noticeable after longer than five hours of milling. However the dissolution of Al in Nb was not completed before the amorphization. No intermetallic phase formed during the mechanical alloying. Before complete amorphization, metastable nitride of Nb_4.62N_2.14 (i.e., -NbN) with hexagonal structure has formed in nanocrystalline size through nitrogen incorporation from ambient environment. The lattice parameter of Nb increased significantly (up to 3.3433 Å after 5 hours of milling) during the milling. Upon annealing above 950 °C, Nb₂Al became the dominant feature with the -NbN, and Nb₃Al did not form from the samples milled at ambient environment. Nb₃Al appeared only from a sample milled at Ar environment. Structural evolution during mechanical alloying of the Nb-Al system is critically dependent the upon milling environment.     

Thermal and mechanically activated decomposition of LiAlH4

Thermal stability of as-received LiAlH₄ and milled LiAlH₄ has been investigated. The thermal decomposition mechanism of as-received LiAlH₄ depends on the temperature-time history. Apparent activation energies and enthalpies of the reactions have been obtained. During milling treatment, the high temperature and pressures locally induced by shocks lead to LiAlH₄ mechanically decomposition. The decomposition temperatures of LiAlH₄ and Li₃AlH₆ are both reduced by ∼60 °C due to particle size reduction produced by mechanical milling. Besides, the activation energy of the decomposition reaction of LiAlH₄ decreases as compared to as-received LiAlH₄. Moreover, a layer of oxide (∼5 nm) at the surface of the milled alanate Li₃AlH₆ is observed. This layer could have a drastic influence on decomposition H-kinetics.     

Development of alkali activated cement from mechanically activated silico-manganese (SiMn) slag

Silico-manganese (SiMn) slag has been used to develop alkali activated cement binder. The reactivity of SiMn slag was altered by mechanical activation using eccentric vibratory and attrition mill. The reaction kinetics during alkali activation of SiMn slag and structural reorganization were studied using isothermal conduction calorimetry and Fourier transform infrared spectroscopy. The particle size after milling was smaller in attrition milled samples but reaction started earlier in vibratory milled samples due to more reactivity. This observation was further supported by compressive strength which was highest in samples prepared from vibratory milled slag. The main reaction product was C–S–H (C = CaO, S = SiO₂, H = H₂O) of low crystallinity of different types with varying Si/Al and Ca/Si ratio. An attempt has been made to relate the microstructure with mechanical properties. The results obtained in this study establish technical suitability of SiMn slag as raw material for alkali activated cement.     

Microstructural,physical, and mechanical characteristics of bulk nanocrystalline copper synthesised using powder metallurgy

Abstract

In the present study, elemental Cu powder was mechanically milled to reduce the grain (crystalline) size to the nanorange (< 100 nm). The powder was consolidated by die cold compaction. Omitting the sintering process, the powder compacts of 10 h mechanically milled powder and elemental powder without mechanical milling (0 h mechanically milled) were hot extruded at different temperatures to maintain a crystallite size within the nanoregime. Characterisation revealed that samples with relatively lower grain size (63 nm/10 h mechanically milled) exhibited reduced density and ductility, similar dimensional stability, and significantly enhanced hardness, 0.2% yield strength, and ultimate tensile strength. Particular emphasis was placed on correlating the properties of the samples with their microstructural features.     

Al–Cu–Fe coatings manufactured by the flame spraying process

Two-hour milled (activated) Al–20Cu–15Fe (at%) powders were subjected to annealing at 600°C for 1?h. The phase and microstructural evolutions were characterized by X-ray diffractometry and scanning electron microscopy. Al₇Cu₂Fe and Al₆₀Cu₃₀Fe₁₀ phases were formed after annealing. Both annealed and milled powders were consolidated using the flame spraying process. In both cases, FeAl(Cu) was the major phase while some oxides and α-Fe(Al,Cu) were also found. The coating produced from the milled powder was severely cracked and showed higher oxide content. The coating prepared from the annealed powder showed better quality. It was annealed at 600°C for 1?h to investigate the thermal stability of the various phases. All phases persevered after annealing while the Fe₂Al₅ phase was formed as a new phase.     

Fabrication and characterisation of copper–alumina nanocomposites prepared by high-energy fast milling

Two different methods are used to prepare Cu–20 vol-% Al₂O₃ nanocomposite powders via high-energy planetary fast milling. In the solid solution method, CuO powder was added to the Cu–Al solid solution powder, and the composite was fabricated by milling after 100?h. In the direct mixing method, Cu and Al₂O₃ powders were mechanically milled via high-energy planetary fast milling for 100?h. The transition electron micrographs (dark and white fields) revealed the presence of Al₂O₃ nanoparticles in crystalline Cu matrices for both methods. However, the density and bending strength of the nanocomposites produced via the solid solution method were higher than those of the samples produced via the direct mixing method.     

Effects of attrition milling and post-sintering heat treatment on fabrication,microstructure and properties of transformation toughened ZrO2

The effect of attrition milling and post-sintering heat treatment on the fabrication, phase relations, microstructure and properties of ZrO₂ (+2.3vol% Y₂O₃) powder used to produce a transformation toughened material was examined. Powder used to fabricate the unmilled material was treated and consolidated by a colloidal method. The same powder, treated and consolidated by the same method, but ball milled in a commercial alumina mill before consolidation, was used to fabricate the milled material. Both materials were sintered at 1400° C for 1 h and then heat treated at higher temperatures. Milling introduced Al₂O₃ inclusions (< 1 vol%) and a glass phase (7 to 10 vol%). The milled powder was more difficult to sinter and exhibited more bloating (density decrease) during subsequent heat treatment. Transmission electron microscopy observations indicated that the larger glass content of the milled material beneficially reduced residual stresses that arose due to thermal contraction anistropy. Post-sintering heat treatment at temperatures > 1450° C produced detectable amounts of cubic ZrO₂ consistent with previously reported phase studies of the ZrO₂-Y₂O₃ system. The development of a bimodal grain structure was concurrent with the formation of detectable cubic phase. The larger grains in this bimodal distribution were primarily observed on the external surface and co-ordinating pores produced during the post-sintering heat treatments which were responsible for the bloating phenomenon. It is hypothesized that the pores were produced by the release of high pressure oxygen during cubic phase formation. Both fracture toughness (K _c) and hardness of the as-sintered materials were unaffected by milling. Hardness decreased with bloating and the decrease was more pronounced for the milled material which exhibited more bloating.     

Simultaneous carbothermic reduction of iron and titanium oxides to produce an iron-based composite by mechanically activated sintering method

In this research, for the first time, Fe–TiC nano-crystalline composite was produced via simultaneous reduction of iron and titanium oxides by petrocoke. Powder mixture of Fe₂O₃/TiO₂/petrocoke was mechanically activated in a high-energy ball mill at different times. X-ray diffraction method (XRD) and Scanning Electron Microscopy (SEM) were used to characterize the milled powders. The results showed that new phases were not formed during milling, even after 20 h of milling. However, crystallite size and lattice strain of hematite were remarkably decreased and increased, respectively. Thermogravimetry and Differential Thermal Analysis (TG–DTA) were done on 0, 10 and 20 h mechanically activated powders. These experiments showed a substantial decrease in reduction temperature of iron and titanium oxides as a result of mechanical activation. Then, the powders were cold compacted and sintered at 1200 °C in argon atmosphere for 1 h. XRD results of 20 h milled samples demonstrated that, in this condition, iron oxide was completely reduced to nano-crystalline iron and titanium dioxide was reduced to nano-crystalline titanium carbide and Fe–TiC nano-crystalline composite was successfully formed.     

Tribological properties of Al6061–Al2O3 nanocomposite prepared by milling and hot pressing

Tribological properties of bulk Al6061–Al₂O₃ nanocomposite prepared by mechanical milling and hot pressing were investigated. Al6061 chips were milled for 30 h to achieve a homogenous nanostructured powder. A 3 vol.% Al₂O₃ nanoparticles (∼30 nm) were added to the Al6061 after 15 and 30 h from the beginning of milling. The milling times with Al₂O₃ in these two samples were then 15 h and 30 min, respectively. Additionally, 3 vol.% Al₂O₃ (1 μm and 60 μm) was added to the Al6061 after 15 h of milling; where, the micron size Al₂O₃ in these two samples, was milled 15 h with the matrix. Hot pressing of milled samples was executed at 400 °C under 128 MPa pressure in a uniaxial die. The hot pressed samples were characterized by micro-hardness test, bulk density measurements, pin on disc wear test, and finally scanning electron microscopy observations. Fifteen hour-milled nanocomposite with nanoscale Al₂O₃, showed improvement in wear resistance and bulk density compared with that of 30 min-milled nanocomposites due to better dispersion of Al₂O₃ nanoparticles, improved surface quality of nanocomposite particles before pressing and more grain refinement of Al matrix. Moreover, increasing the reinforcement size increased the wear rate because of reduction in relative density, hardness and inter-particle spacing.     

Thermal stability and phase formation of mechanically alloyed Ti-Al-Si-C powders

Two quarternary Ti-Al-Si-C powder mixtures, 55Ti-27Al-12Si-6C and 55Ti-36Al-6Si-3C, were mechanically alloyed. The as-alloyed and heated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). XRD patterns showed diffuse halos of amorphous like phase for 20-40 h milled powders, but TEM examinations demonstrated that the 40 h milled powders were mainly composed of Ti solid solutions, with some amount of amorphous phase. SEM observations displayed that the lamellar structures of Ti and Al formed at the early stage of milling process subsequently led to the formation of nano- or sub-micrometer particles of homogeneous composition after prolonged milling to 40 h. It is deduced that the solid-stated reaction by inter-diffusion of components should be responsible for phase formation during mechanical alloying. DSC curves of the 40 h milled powders exhibited two sharp exothermal peaks, and the investigation on thermal stability of the 40 h milled powders indicated that Ti₅Si₃ was first formed at lower temperature, followed by Al₂Ti₄C₂and TiC at intermediate temperature (820°C), and these phases were stable at elevated temperatures. These results raise the possibility of synthesizing TiAl-based composite with titanium silicides and titanium carbides as reinforcements by proper selection of powder compositions.     

Structural,Thermal and Magnetic Properties of Nanocrystalline Co<Subscript>80</Subscript>Ni<Subscript>20</Subscript> Alloy Prepared by Mechanical Alloying

Co₈₀Ni₂₀ powder mixture was mechanically alloyed by high-energy planetary ball milling, starting from elemental Co and Ni metal powders. The morphological, microstructural, thermal and magnetic properties of the milled powders were characterised respectively by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and vibratory sample magnetometry. In addition to a highly disordered phase, two face-centred cubic (FCC) and hexagonal close-packed (HCP), solid solutions, FCC Co(Ni), FCC Ni(Co) and HCP Co(Ni), are observed after 3 h of milling. Their grain sizes decrease with increase in milling time attaining, at 48 h of milling, 12 nm, 25 nm and 10 nm, respectively. Beyond a certain milling time, no further refinement of the microstructure occurs and the morphological equilibrium is usually given by a bimodal particle size distribution. Magnetic measurements of the milled Co₈₀Ni₂₀ alloy powder exhibit a soft ferromagnetic character where the magnetic parameters are sensitive to the milling time mainly due to the particle size refinement as well as the formation of Co(Ni) and Ni(Co) solid solutions. Both the saturation magnetisation ( M _s) and coercivity ( H _c) were found to decrease with milling time, attaining the values of M _s = 126 emu/g and H _c = 60 Oe after 48 h of milling.     

Synthesis and characterisation of nanostructured Al–Al3V and Al–(Al3V–Al2O3) composites by powder metallurgy

In this study, the formation and characterisation of Aluminium (Al)-based composites by mechanical alloying and hot extrusion were investigated. Initially, the vanadium trialuminide (Al₃V) particles with nanosized structure were successfully produced by mechanical alloying and heat treatment. Al₃V–Al₂O₃ reinforcement was synthesised by mechanochemical reduction during milling of V₂O₅ and Al powder mixture. In order to produce composite powders, reinforcement powders were added to pure Al powders and milled for 5?h. The composite powders were consolidated in an extrusion process. The results showed that nanostructured Al-10?wt-% Al₃V and Al-10?wt-% (Al₃V–Al₂O₃) composites have tensile strengths of 209 and 226?MPa, respectively, at room temperature. In addition, mechanical properties did not drop drastically at temperatures of up to 300°C.     

Al2O3和 Y2O3包覆的 SiC复合粒子制备

本文利用非均匀成核法, 将Al(OH)     

Effect of preliminary high-energy ball milling on the structural-phase state and microhardness of Ni3Al samples obtained by spark plasma sintering

The study of the influence of the duration of preliminary high-energy ball milling on the features of the structural-phase state and the level of microhardness of consolidated Ni₃Al samples obtained by the method of spark plasma sintering has been carried out. It was found that the inhomogeneous state of the precursor from the 3Ni-Al powder mixture in the case of preliminary ball milling of a short duration (1 min) is a cause of the formation of an inhomogeneous structural-phase state of the consolidated Ni₃Al sample. An increase in the duration of high-energy ball milling provides a homogeneous phase composition, promotes the refinement of the grain structure and an increase in the microhardness values of the obtained Ni₃Al samples. The main factors determining the processes of structural-phase transformation during the formation of Ni₃Al under the conditions of spark plasma sintering, depending on the preliminary high-energy ball milling, are revealed. It is shown that grain boundary strengthening is the one of the effective mechanisms for increasing the strength of the material under study.     

Carbon dioxide reduction into carbon by mechanically milled wustite

The CO₂ decomposition utilizing mechanically milled wustite powders was qualitatively and quantitatively examined and its mechanism was investigated. The wustite phase is stable at least up to 6 h of milling, and the lattice parameter, the crystallite size and the average particle diameter are monotonously decreased with milling time, while the BET specific surface area is correspondingly increased. The mechanically milled FeO powder decomposes CO₂ into graphite and amorphous carbon at 773 K, where the decomposition intensity increases with milling time, while unmilled FeO decomposes CO₂ into CO with the same annealing condition. It is found that the FeO powder thermally decomposes into Fe and Fe₃O₄ prior to the reaction with CO₂, followed by the precipitated Fe reacting with CO₂, and also that the thermal decomposition is promoted by the milling process.     

Synthesis of Fe3N by mechano-chemical reactions between iron and organic H x (CN)6 ring compounds

Novel mechanically activated solid state synthesis reactions between elemental Fe powder and amine compounds-piperazine (Hi₁₀C₄N₂) and pyrazine (H₄C₄N₂) — have been studied. Powder samples prepared after 144 and 228 h of ball milling in vacuum were examined by X-ray diffraction, scanning electron microscopy and thermal analysis methods. After ball milling for a time brief compared to that required for most solid state-gas reactions formation of a crystalline iron nitride (Fe₃N) a predominant phase with nitrogen concentration up to ca. 9.0 wt% was observed. Thermal analysis experiments showed structural stability of the Fe₃N phase up to ca. 720 K. In the final product a small residual fraction was formed from Fe and carbon dispersed during mechanical processing. The concentration of carbon in this fraction, estimated from thermogravimetric analysis was up to 2.5 wt%, dependent on milling conditions and the organic compound used. Mechanochemical synthesis, reaction effectiveness, product composition and particle morphology depends on the milling time and chemical characteristics of the organic compound used. Fine Fe₃N particles at a submicrometre size range were obtained only by milling with pyrazine. Further, the higher chemical reactivity of pyrazine than piperazine was confirmed through the higher level of nitridation achieved in the same preparation time.     

Material and Energy Interactions between Milling Bodies,Milled Particles,and Milling Environment

Changes in particle size, surface state, and composition brought about by planetary and vibration milling of silicon and quartz in various permittivity liquids were investigated. Using a variety of spectroscopic techniques (IRS, XPS, and Mössbauer spectroscopy) the changes in quality of the superficial layers of milled particles have been determined. During energy-intensive milling, the material being milled intensively interacts with the media and milling environment. The nature of the interaction and quality of the surface shell covering the milled particles depend on the reactivity and hardness of the interacting solids and of the milling environment. During planetary milling of silicon with tungsten carbide media, the superficial layers are formed by silicon suboxides and silicon oxide. The thickness of the superficial layer and the share of SiO₂ increase with increasing permittivity of liquids. Milling with steel media results in a more complicated composition of the superficial layer. According to Mössbauer spectra, the iron is present in two main forms: as a magnetically ordered form identical with basic material of balls and in a paramagnetic form as a product of a mechanically stimulated surface reaction between Si and Fe. The presence of the superficial layers on the milled particles of silicon and quartz markedly influences the values of the specific surface area. This influence should be taken into consideration when calculating the specific contamination of the milled powder.